This invention relates to circuitry for controlling an electrically powered door and, more particularly, to a control circuit for converting motor operators not so designed originally to a system which will prevent further powering of the door in its closing direction should there be an obstruction in the path of movement of the closing door. More specifically, the invention relates to a control circuit adapted to accommodate an obstruction sensing device, such as a safety edge, and which when connected to a motor operator not so equipped converts it into one that reverses powering of the door should it engage an obstruction while closing.
Electrical sensing strips have long been used as safety edges for electrically powered doors, movable walls, curtains and the like to provide safe operation. An obstruction, such as a person or an object, in the closure path of the door or wall causes deformation of the strip and closure of an electrical contact which, in turn, causes immediate deenergization or reversal of the drive motor. Thus, injury to a person or damage to an object obstructing closure of the door is prevented.
Motor operators for electrically powered doors equipped with a safety edge require special wiring, typically consisting of a double pole double throw relay whose coil is activated by closure of a contact in the safety edge. One set of normally closed contacts on this relay is connected in series with the closed coil of the reversing controller and the other set of contacts, which are normally open, is connected in parallel with the OPEN button. Activation of this relay by closure of the electrical contact in the safety edge by engagement with an obstruction stops further powering in the closing direction, reverses the direction of door movement and powers the door to the full open position. Relay activation by the safety edge coming in contact with the floor is prevented by a normally closed limit switch connected in series with the relay coil that opens just before the door strikes the floor. This also prevents activation of the door by the sensing device after it has been completely closed; this is important from the security standpoint because sensing devices typically used in safety edges can be actuated from the outside. Single phase motor operators require instant reverse motors, quick reverse motors, or some special circuitry to guarantee that the motor will not continue to run in the closing direction even though the reversing controller has switched contacts. Should this occur, the limit switches in series with the relay coil on the reversing controller would no longer be in the proper circuit and the motor operator would not shut itself off.
While there is widespread use of door operators which incorporate obstruction sensing devices, there is also a large population of motor operators for electrically powered doors and gates which do not have, and were not designed to accommodate, an obstruction-sensing device in an edge of the door or gate. The majority of standard operators for commercial/industrial doors and gates utilize 24 volts A.C. as a control voltage, have normally closed limit switches in the control circuit for providing positional reference, and two or three push buttons (OPEN, CLOSE) or (OPEN, CLOSE and STOP) provide the person-machine interface.
In the interest of safer operation, it would be desirable if such operators, too, were capable of immediately stopping door closure, and reopening or reversing upon engaging an obstruction. However, because the circuitry required to accomplish the reversing function is relatively more complex than, and generally incompatible with, the simple pushbutton control circuitry of standard operators, it is difficult to alter such operators, at a commercially feasible cost, so as to be capable of reversing when the door engages an obstruction.
A primary object of the present invention is to provide a circuit adapted to accommodate an obstruction-sensing device and which when connected to a motor operator not so equipped converts it into one that reverses powering of a door or gate upon engaging an obstruction while closing.
Another object is to provide such a circuit which can easily be connected to the motor operator without having to analyze the control protocol or modify the circuitry of the operator in question.
A more specific object of the invention is provide a reversing circuit which is universally adapted to retrofit any manually operated 24 volt A.C. motor operator for electrically powered commercial/industrial doors and gates.
Another object is to provide a reversing circuit as described in the preceding paragraph which is universal in the additional respect of being adapted to accommodate therein any obstruction sensing device which provides a dry normally open contact.